For some time, the religious right has decried "secular humanism," a philosophy that rejects the supernatural or spiritual as a basis for moral decisionmaking. But now, nonbelievers are vigorously fighting back.

Only a small percentage of Americans admit to being nontheists (between 2 and 9 percent, depending on the poll), but that equates to many millions. And religionists' role in debates over stem-cell research and evolution vs. intelligent design – as well as radical religion in world conflicts – have galvanized some atheists to mount a counteroffensive.

In bestselling books, on websites, and with a national lobbying effort, atheists and other nontheists are challenging the growing religious influence in government and public life. Some are attacking the foundations of religion itself.

Two particularly provocative books, in fact, hit the top of Publishers Weekly's religion bestseller list in December. No. 1, "The God Delusion," by evolutionary biologist Richard Dawkins, and No. 2, "Letter to a Christian Nation," by writer Sam Harris, are no-holds-barred, antireligion polemics that call for the eradication of all manifestations of faith.

"I am attacking God, all gods, anything and everything supernatural, wherever and whenever they have been or will be invented," declares Dr. Dawkins, the famed Oxford professor who wrote "The Selfish Gene."

These offerings are so intolerant of religion of any kind – liberal, moderate, or fundamentalist – that some scientists and secularists have critiqued their peers for oversimplification and for a secular fundamentalism.

"They undermine their own case by writing in a language that suffers from many things they say are true of believers – intolerance, disrespect, extremism," says Alan Wolfe, a professor of religion at Boston College, who is a secularist and author of several books on American religious perspectives.

Yet the authors are anything but modest about their efforts to supplant faith with pure scientific rationality. While critics point out that religion is a genuine reflection of people's experience and will always exist, Mr. Harris suggests it could be equated with slavery, which once was widely acceptable, but eventually was looked upon with horror. He sees it as responsible for many of life's tragedies.

Harris first hit the bestseller bull's-eye in 2004 with "The End of Faith," and he says the responses to that book, particularly those from Christians, spurred his latest epistle.

A mere 96 pages, "Letter" may be dismissed by many for its condescending tone or overheated rhetoric. Yet its bold arguments offer a useful window into nontheist perspectives and could also startle some complacent religionists into a rethinking and refining of perceptions.

Many nontheists don't share this militant perspective, but have decided that keeping silent in religious America no longer makes sense. They are astonished that a majority of Americans question evolution and support teaching intelligent design in the science classroom. They are distressed over polls that show that at least half of Americans are unwilling to vote for an atheist despite the Constitution's requirement that there be no religious test for public office. And they contend that in recent years, Congress has passed bills and the president has issued executive orders that have privileged religion in inappropriate and unconstitutional ways.

As a result, seven organizations of nontheists – including atheists, freethinkers, humanists, and agnostics – began the Secular Coalition for America (SCA), a lobby seeking to increase the visibility and respectability of nontheistic viewpoints in the United States.

"In some parts of the country, children are ostracized if someone finds out their families are atheists," says Lori Lipman Brown, SCA director. "We need to educate the public that people who don't have a god belief can be good neighbors and friends and moral and ethical people."

They also intend to stand up vigorously for their rights. "Some people want to go back to a time when religion was imposed, such as official prayer in public schools," she adds. "For someone to say they can't practice their religion appropriately if all schoolchildren are not required to recite a public prayer is very disturbing."

The SCA intends to lobby the new Congress to override a presidential veto on stem-cell research and to repeal land-use legislation and other laws seen as "privileging one religion over other religions or over those who don't follow religion."

Still, the group makes clear on its website that while it promotes reason and science as the bases for policymaking, it also supports religious tolerance.

"I have absolutely no problem with anyone believing differently than I believe, as long as they don't impose their religion on me or my government," says Ms. Brown, a former Nevada state senator.

To spotlight the prejudice against atheists holding public office – and to encourage atheists to "come out of the closet," SCA is sponsoring a contest to identify the highest US official who acknowledges being a nonbeliever. They expect to announce contest results in February.

Internet-based groups are also seeking to spread the atheist message, particularly among young adults. The Rational Response Squad (RRS) has chosen a provocative mode using the popular website YouTube. Their "blasphemy challenge" calls on young nonbelievers to create videos in which they renounce belief in the "sky God of Christianity" and upload it on the site; in return they'll receive a free documentary DVD, "The God Who Wasn't There," which includes interviews with Dawkins, Harris, and others. RRS is publicizing its campaign on 25 popular teen websites.

"We wanted to strike up more of a conversation about religion, and this was a way for people to show their nonbelief and encourage others to come out," says Brian Sapient, RRS cofounder.

Mr. Sapient says he was raised Catholic and then a born-again Christian, but later learned that many things he was taught were fictional. RRS now has some 20,000 people on message boards, with about 5,000 actively engaged in debunking religious claims, passing out fliers, and placing DVDs in churches.

As for the blasphemy challenge, "there's about 490 response videos so far, and 85,000 views on our trailer video," he says. Sapient acknowledges this approach may not persuade religious youths. "There are people with a more palatable approach to talking about religion," he says, "but I wonder if those people would be as effective if it weren't for us or Sam Harris or Richard Dawkins shaking up the group a bit."

He also insists that you don't really respect people unless you speak up when you think their beliefs are wrong. It's OK with him, he adds, if religious people try to convince him they are right.

Harris and Dawkins make it clear that they think faith has gotten off too easy for too long. Their books have spurred widespread commentary, much of it a strong critique of their arguments and lack of religious knowledge. But in a culture immersed in combativeness in politics and the media, the intemperate books are selling well.

Yet one critic, New York Times columnist Nicholas Kristof, calls for a truce: "We've suffered enough from religious intolerance that the last thing the world needs is irreligious intolerance."